Detection of infrared radiation emitted by warm bodies provides an important method for night vision (perception without visible light). Infrared detectors may be classified in various ways, such as scanning or staring arrays, cryogenic (typically liquid nitrogen temperatures) or uncooled detectors, 3-5 micron or 8-12 micron spectral sensitivity range, and photon or thermal detection mechanism. For portable, low power applications where the greater detectivity of cryogenic detectors is not needed, the preferred choice is an uncooled thermal detector: infrared photons are absorbed and the resultant heating of the absorbing element is detected. The thermal detector is usually one of three types: (1) pyroelectric detector, (2) thermocouple, or (3) bolometer.
In the operation of an infrared (IR) image sensing array, the desired output signal is obtained from the difference between two consecutive array outputs. The first output is obtained with the IR image deliberately defocused on the array and is used to determine the background flux associated with the scene. The second output is obtained with the image sharply focused on the array.
Typically, the signals from either the dark frame or from both frames are digitized and stored in memory for subsequent signal processing operation. This analog to digital conversion and storage memory add to the cost and complexity of the overall imaging system.
Accordingly, improvements which overcome any or all of the problems are presently desirable.